In some diagnostic and therapeutic techniques, a catheter is inserted into a chamber of the heart and brought into contact with the inner heart wall. For example, intracardiac radio-frequency (RF) ablation is a known method to treat cardiac arrhythmias. In this technique, a catheter having an electrode at its distal tip is inserted through the patient's vascular system into a chamber of the heart. The electrode is brought into contact with a site (or sites) on the endocardium, and RF energy may be applied through the catheter to the electrode in order to ablate the heart tissue at the site. Excessive contact force (or pressure) and/or excessive RF energy, however, may cause undesired damage to the heart tissue and even perforation of the heart wall. As such, proper contact between the electrode and the endocardium is necessary in order to achieve the desired diagnostic function and therapeutic effect of the catheter.
Various techniques exist for verifying electrode contact with tissue. For example, U.S. Pat. No. 6,695,808, whose disclosure is incorporated herein by reference, describes apparatus for treating a selected patient tissue or organ region. A probe has a contact surface that may be urged against the region, thereby creating contact force or contact pressure. A pressure transducer measures the contact pressure and supplies information about the existence and magnitude of the contact force to the user of the instrument.
As another example, U.S. Pat. No. 6,241,724, whose disclosure is incorporated herein by reference, describes methods for creating lesions in body tissue using segmented electrode assemblies. In one embodiment, an electrode assembly on a catheter carries pressure transducers, which sense contact with tissue and convey signals to a pressure contact module. The module identifies the electrode elements that are associated with the pressure transducer signals and directs an energy generator to convey RF energy to these elements, and not to other elements that are in contact only with blood.
Another example is presented in U.S. Pat. No. 6,915,149, whose disclosure is incorporated herein by reference. This patent describes a method for mapping a heart using a catheter having a tip electrode for measuring the local electrical activity. In order to avoid artifacts that may arise from poor tip contact with the tissue, the contact pressure between the tip and the tissue is measured using a pressure sensor to ensure stable contact.
U.S. Pat. No. 8,162,935, whose disclosure is incorporated herein by reference, describes systems and methods for assessing electrode-tissue contact for tissue ablation. An electro-mechanical sensor within the catheter shaft generates electrical signals corresponding to the amount of movement of the electrode within a distal portion of the catheter shaft. An output device receives the electrical signals for assessing a level of contact between the electrode and a tissue.
U.S. Pat. No. 8,357,152, whose disclosure is incorporated herein by reference, describes systems and methods for measuring the contact pressure applied to a tip of a catheter using a magnetic field sensor in the tip and a magnetic field generator within the probe. The magnetic field sensor generates signals in response to the magnetic field generator within the probe, which are processed to determine the position of the tip relative to the position of the magnetic field generator, thereby indicating the amount of deformation of the tip and thus the pressure applied to the tip.
U.S. Pat. App. Pub. No. 2014/0187917, the entire disclosure of which is incorporated herein by reference, describes a catheter that carries a miniature transmitting coil and three sensing coils on opposing portions of a flexibly-jointed distal tip section. The transmitting coil is aligned with the longitudinal axis of the catheter and three sensing coils are also aligned with the longitudinal axis but positioned at an equal distance from the transmitting coil, and at equally-spaced radial positions about the longitudinal axis of the catheter. The miniature transmitting coil generates a magnetic field sensed by the three sensing coils which generate signals representative of axial displacement and angular deflection between the opposing portions of the distal tip section.